xref: /linux/drivers/pci/of.c (revision 7fe03f8ff55d33fe6398637f78a8620dd2a78b38)

// SPDX-License-Identifier: GPL-2.0+
/*
 * PCI <-> OF mapping helpers
 *
 * Copyright 2011 IBM Corp.
 */
#define pr_fmt(fmt)	"PCI: OF: " fmt

#include <linux/cleanup.h>
#include <linux/irqdomain.h>
#include <linux/kernel.h>
#include <linux/pci.h>
#include <linux/of.h>
#include <linux/of_irq.h>
#include <linux/of_address.h>
#include <linux/of_pci.h>
#include <linux/platform_device.h>
#include "pci.h"

#ifdef CONFIG_PCI
/**
 * pci_set_of_node - Find and set device's DT device_node
 * @dev: the PCI device structure to fill
 *
 * Returns 0 on success with of_node set or when no device is described in the
 * DT. Returns -ENODEV if the device is present, but disabled in the DT.
 */
int pci_set_of_node(struct pci_dev *dev)
{
	if (!dev->bus->dev.of_node)
		return 0;

	struct device_node *node __free(device_node) =
		of_pci_find_child_device(dev->bus->dev.of_node, dev->devfn);
	if (!node)
		return 0;

	struct device *pdev __free(put_device) =
		bus_find_device_by_of_node(&platform_bus_type, node);
	if (pdev)
		dev->bus->dev.of_node_reused = true;

	device_set_node(&dev->dev, of_fwnode_handle(no_free_ptr(node)));
	return 0;
}

void pci_release_of_node(struct pci_dev *dev)
{
	of_node_put(dev->dev.of_node);
	device_set_node(&dev->dev, NULL);
}

void pci_set_bus_of_node(struct pci_bus *bus)
{
	struct device_node *node;

	if (bus->self == NULL) {
		node = pcibios_get_phb_of_node(bus);
	} else {
		node = of_node_get(bus->self->dev.of_node);
		if (node && of_property_read_bool(node, "external-facing"))
			bus->self->external_facing = true;
	}

	device_set_node(&bus->dev, of_fwnode_handle(node));
}

void pci_release_bus_of_node(struct pci_bus *bus)
{
	of_node_put(bus->dev.of_node);
	device_set_node(&bus->dev, NULL);
}

struct device_node * __weak pcibios_get_phb_of_node(struct pci_bus *bus)
{
	/* This should only be called for PHBs */
	if (WARN_ON(bus->self || bus->parent))
		return NULL;

	/*
	 * Look for a node pointer in either the intermediary device we
	 * create above the root bus or its own parent. Normally only
	 * the later is populated.
	 */
	if (bus->bridge->of_node)
		return of_node_get(bus->bridge->of_node);
	if (bus->bridge->parent && bus->bridge->parent->of_node)
		return of_node_get(bus->bridge->parent->of_node);
	return NULL;
}

struct irq_domain *pci_host_bridge_of_msi_domain(struct pci_bus *bus)
{
#ifdef CONFIG_IRQ_DOMAIN
	struct irq_domain *d;

	if (!bus->dev.of_node)
		return NULL;

	/* Start looking for a phandle to an MSI controller. */
	d = of_msi_get_domain(&bus->dev, bus->dev.of_node, DOMAIN_BUS_PCI_MSI);
	if (d)
		return d;

	/*
	 * If we don't have an msi-parent property, look for a domain
	 * directly attached to the host bridge.
	 */
	d = irq_find_matching_host(bus->dev.of_node, DOMAIN_BUS_PCI_MSI);
	if (d)
		return d;

	return irq_find_host(bus->dev.of_node);
#else
	return NULL;
#endif
}

bool pci_host_of_has_msi_map(struct device *dev)
{
	if (dev && dev->of_node)
		return of_get_property(dev->of_node, "msi-map", NULL);
	return false;
}

static inline int __of_pci_pci_compare(struct device_node *node,
				       unsigned int data)
{
	int devfn;

	devfn = of_pci_get_devfn(node);
	if (devfn < 0)
		return 0;

	return devfn == data;
}

struct device_node *of_pci_find_child_device(struct device_node *parent,
					     unsigned int devfn)
{
	struct device_node *node, *node2;

	for_each_child_of_node(parent, node) {
		if (__of_pci_pci_compare(node, devfn))
			return node;
		/*
		 * Some OFs create a parent node "multifunc-device" as
		 * a fake root for all functions of a multi-function
		 * device we go down them as well.
		 */
		if (of_node_name_eq(node, "multifunc-device")) {
			for_each_child_of_node(node, node2) {
				if (__of_pci_pci_compare(node2, devfn)) {
					of_node_put(node);
					return node2;
				}
			}
		}
	}
	return NULL;
}
EXPORT_SYMBOL_GPL(of_pci_find_child_device);

/**
 * of_pci_get_devfn() - Get device and function numbers for a device node
 * @np: device node
 *
 * Parses a standard 5-cell PCI resource and returns an 8-bit value that can
 * be passed to the PCI_SLOT() and PCI_FUNC() macros to extract the device
 * and function numbers respectively. On error a negative error code is
 * returned.
 */
int of_pci_get_devfn(struct device_node *np)
{
	u32 reg[5];
	int error;

	error = of_property_read_u32_array(np, "reg", reg, ARRAY_SIZE(reg));
	if (error)
		return error;

	return (reg[0] >> 8) & 0xff;
}
EXPORT_SYMBOL_GPL(of_pci_get_devfn);

/**
 * of_pci_parse_bus_range() - parse the bus-range property of a PCI device
 * @node: device node
 * @res: address to a struct resource to return the bus-range
 *
 * Returns 0 on success or a negative error-code on failure.
 */
static int of_pci_parse_bus_range(struct device_node *node,
				  struct resource *res)
{
	u32 bus_range[2];
	int error;

	error = of_property_read_u32_array(node, "bus-range", bus_range,
					   ARRAY_SIZE(bus_range));
	if (error)
		return error;

	res->name = node->name;
	res->start = bus_range[0];
	res->end = bus_range[1];
	res->flags = IORESOURCE_BUS;

	return 0;
}

/**
 * of_get_pci_domain_nr - Find the host bridge domain number
 *			  of the given device node.
 * @node: Device tree node with the domain information.
 *
 * This function will try to obtain the host bridge domain number by finding
 * a property called "linux,pci-domain" of the given device node.
 *
 * Return:
 * * > 0	- On success, an associated domain number.
 * * -EINVAL	- The property "linux,pci-domain" does not exist.
 * * -ENODATA	- The linux,pci-domain" property does not have value.
 * * -EOVERFLOW	- Invalid "linux,pci-domain" property value.
 *
 * Returns the associated domain number from DT in the range [0-0xffff], or
 * a negative value if the required property is not found.
 */
int of_get_pci_domain_nr(struct device_node *node)
{
	u32 domain;
	int error;

	error = of_property_read_u32(node, "linux,pci-domain", &domain);
	if (error)
		return error;

	return (u16)domain;
}
EXPORT_SYMBOL_GPL(of_get_pci_domain_nr);

/**
 * of_pci_preserve_config - Return true if the boot configuration needs to
 *                          be preserved
 * @node: Device tree node.
 *
 * Look for "linux,pci-probe-only" property for a given PCI controller's
 * node and return true if found. Also look in the chosen node if the
 * property is not found in the given controller's node.  Having this
 * property ensures that the kernel doesn't reconfigure the BARs and bridge
 * windows that are already done by the platform firmware.
 *
 * Return: true if the property exists; false otherwise.
 */
bool of_pci_preserve_config(struct device_node *node)
{
	u32 val = 0;
	int ret;

	if (!node) {
		pr_warn("device node is NULL, trying with of_chosen\n");
		node = of_chosen;
	}

retry:
	ret = of_property_read_u32(node, "linux,pci-probe-only", &val);
	if (ret) {
		if (ret == -ENODATA || ret == -EOVERFLOW) {
			pr_warn("Incorrect value for linux,pci-probe-only in %pOF, ignoring\n",
				node);
			return false;
		}
		if (ret == -EINVAL) {
			if (node == of_chosen)
				return false;

			node = of_chosen;
			goto retry;
		}
	}

	if (val)
		return true;
	else
		return false;
}

/**
 * of_pci_check_probe_only - Setup probe only mode if linux,pci-probe-only
 *                           is present and valid
 */
void of_pci_check_probe_only(void)
{
	if (of_pci_preserve_config(of_chosen))
		pci_add_flags(PCI_PROBE_ONLY);
	else
		pci_clear_flags(PCI_PROBE_ONLY);
}
EXPORT_SYMBOL_GPL(of_pci_check_probe_only);

/**
 * devm_of_pci_get_host_bridge_resources() - Resource-managed parsing of PCI
 *                                           host bridge resources from DT
 * @dev: host bridge device
 * @resources: list where the range of resources will be added after DT parsing
 * @ib_resources: list where the range of inbound resources (with addresses
 *                from 'dma-ranges') will be added after DT parsing
 * @io_base: pointer to a variable that will contain on return the physical
 * address for the start of the I/O range. Can be NULL if the caller doesn't
 * expect I/O ranges to be present in the device tree.
 *
 * This function will parse the "ranges" property of a PCI host bridge device
 * node and setup the resource mapping based on its content. It is expected
 * that the property conforms with the Power ePAPR document.
 *
 * It returns zero if the range parsing has been successful or a standard error
 * value if it failed.
 */
static int devm_of_pci_get_host_bridge_resources(struct device *dev,
			struct list_head *resources,
			struct list_head *ib_resources,
			resource_size_t *io_base)
{
	struct device_node *dev_node = dev->of_node;
	struct resource *res, tmp_res;
	struct resource *bus_range;
	struct of_pci_range range;
	struct of_pci_range_parser parser;
	const char *range_type;
	int err;

	if (io_base)
		*io_base = (resource_size_t)OF_BAD_ADDR;

	bus_range = devm_kzalloc(dev, sizeof(*bus_range), GFP_KERNEL);
	if (!bus_range)
		return -ENOMEM;

	dev_info(dev, "host bridge %pOF ranges:\n", dev_node);

	err = of_pci_parse_bus_range(dev_node, bus_range);
	if (err) {
		bus_range->start = 0;
		bus_range->end = 0xff;
		bus_range->flags = IORESOURCE_BUS;
	} else {
		if (bus_range->end > 0xff) {
			dev_warn(dev, "  Invalid end bus number in %pR, defaulting to 0xff\n",
				 bus_range);
			bus_range->end = 0xff;
		}
	}
	pci_add_resource(resources, bus_range);

	/* Check for ranges property */
	err = of_pci_range_parser_init(&parser, dev_node);
	if (err)
		return 0;

	dev_dbg(dev, "Parsing ranges property...\n");
	for_each_of_pci_range(&parser, &range) {
		/* Read next ranges element */
		if ((range.flags & IORESOURCE_TYPE_BITS) == IORESOURCE_IO)
			range_type = "IO";
		else if ((range.flags & IORESOURCE_TYPE_BITS) == IORESOURCE_MEM)
			range_type = "MEM";
		else
			range_type = "err";
		dev_info(dev, "  %6s %#012llx..%#012llx -> %#012llx\n",
			 range_type, range.cpu_addr,
			 range.cpu_addr + range.size - 1, range.pci_addr);

		/*
		 * If we failed translation or got a zero-sized region
		 * then skip this range
		 */
		if (range.cpu_addr == OF_BAD_ADDR || range.size == 0)
			continue;

		err = of_pci_range_to_resource(&range, dev_node, &tmp_res);
		if (err)
			continue;

		res = devm_kmemdup(dev, &tmp_res, sizeof(tmp_res), GFP_KERNEL);
		if (!res) {
			err = -ENOMEM;
			goto failed;
		}

		if (resource_type(res) == IORESOURCE_IO) {
			if (!io_base) {
				dev_err(dev, "I/O range found for %pOF. Please provide an io_base pointer to save CPU base address\n",
					dev_node);
				err = -EINVAL;
				goto failed;
			}
			if (*io_base != (resource_size_t)OF_BAD_ADDR)
				dev_warn(dev, "More than one I/O resource converted for %pOF. CPU base address for old range lost!\n",
					 dev_node);
			*io_base = range.cpu_addr;
		} else if (resource_type(res) == IORESOURCE_MEM) {
			res->flags &= ~IORESOURCE_MEM_64;
		}

		pci_add_resource_offset(resources, res,	res->start - range.pci_addr);
	}

	/* Check for dma-ranges property */
	if (!ib_resources)
		return 0;
	err = of_pci_dma_range_parser_init(&parser, dev_node);
	if (err)
		return 0;

	dev_dbg(dev, "Parsing dma-ranges property...\n");
	for_each_of_pci_range(&parser, &range) {
		/*
		 * If we failed translation or got a zero-sized region
		 * then skip this range
		 */
		if (((range.flags & IORESOURCE_TYPE_BITS) != IORESOURCE_MEM) ||
		    range.cpu_addr == OF_BAD_ADDR || range.size == 0)
			continue;

		dev_info(dev, "  %6s %#012llx..%#012llx -> %#012llx\n",
			 "IB MEM", range.cpu_addr,
			 range.cpu_addr + range.size - 1, range.pci_addr);


		err = of_pci_range_to_resource(&range, dev_node, &tmp_res);
		if (err)
			continue;

		res = devm_kmemdup(dev, &tmp_res, sizeof(tmp_res), GFP_KERNEL);
		if (!res) {
			err = -ENOMEM;
			goto failed;
		}

		pci_add_resource_offset(ib_resources, res,
					res->start - range.pci_addr);
	}

	return 0;

failed:
	pci_free_resource_list(resources);
	return err;
}

#if IS_ENABLED(CONFIG_OF_IRQ)
/**
 * of_irq_parse_pci - Resolve the interrupt for a PCI device
 * @pdev:       the device whose interrupt is to be resolved
 * @out_irq:    structure of_phandle_args filled by this function
 *
 * This function resolves the PCI interrupt for a given PCI device. If a
 * device-node exists for a given pci_dev, it will use normal OF tree
 * walking. If not, it will implement standard swizzling and walk up the
 * PCI tree until an device-node is found, at which point it will finish
 * resolving using the OF tree walking.
 */
static int of_irq_parse_pci(const struct pci_dev *pdev, struct of_phandle_args *out_irq)
{
	struct device_node *dn, *ppnode = NULL;
	struct pci_dev *ppdev;
	__be32 laddr[3];
	u8 pin;
	int rc;

	/*
	 * Check if we have a device node, if yes, fallback to standard
	 * device tree parsing
	 */
	dn = pci_device_to_OF_node(pdev);
	if (dn) {
		rc = of_irq_parse_one(dn, 0, out_irq);
		if (!rc)
			return rc;
	}

	/*
	 * Ok, we don't, time to have fun. Let's start by building up an
	 * interrupt spec.  we assume #interrupt-cells is 1, which is standard
	 * for PCI. If you do different, then don't use that routine.
	 */
	rc = pci_read_config_byte(pdev, PCI_INTERRUPT_PIN, &pin);
	if (rc != 0)
		goto err;
	/* No pin, exit with no error message. */
	if (pin == 0)
		return -ENODEV;

	/* Local interrupt-map in the device node? Use it! */
	if (of_property_present(dn, "interrupt-map")) {
		pin = pci_swizzle_interrupt_pin(pdev, pin);
		ppnode = dn;
	}

	/* Now we walk up the PCI tree */
	while (!ppnode) {
		/* Get the pci_dev of our parent */
		ppdev = pdev->bus->self;

		/* Ouch, it's a host bridge... */
		if (ppdev == NULL) {
			ppnode = pci_bus_to_OF_node(pdev->bus);

			/* No node for host bridge ? give up */
			if (ppnode == NULL) {
				rc = -EINVAL;
				goto err;
			}
		} else {
			/* We found a P2P bridge, check if it has a node */
			ppnode = pci_device_to_OF_node(ppdev);
		}

		/*
		 * Ok, we have found a parent with a device-node, hand over to
		 * the OF parsing code.
		 * We build a unit address from the linux device to be used for
		 * resolution. Note that we use the linux bus number which may
		 * not match your firmware bus numbering.
		 * Fortunately, in most cases, interrupt-map-mask doesn't
		 * include the bus number as part of the matching.
		 * You should still be careful about that though if you intend
		 * to rely on this function (you ship a firmware that doesn't
		 * create device nodes for all PCI devices).
		 */
		if (ppnode)
			break;

		/*
		 * We can only get here if we hit a P2P bridge with no node;
		 * let's do standard swizzling and try again
		 */
		pin = pci_swizzle_interrupt_pin(pdev, pin);
		pdev = ppdev;
	}

	out_irq->np = ppnode;
	out_irq->args_count = 1;
	out_irq->args[0] = pin;
	laddr[0] = cpu_to_be32((pdev->bus->number << 16) | (pdev->devfn << 8));
	laddr[1] = laddr[2] = cpu_to_be32(0);
	rc = of_irq_parse_raw(laddr, out_irq);
	if (rc)
		goto err;
	return 0;
err:
	if (rc == -ENOENT) {
		dev_warn(&pdev->dev,
			"%s: no interrupt-map found, INTx interrupts not available\n",
			__func__);
		pr_warn_once("%s: possibly some PCI slots don't have level triggered interrupts capability\n",
			__func__);
	} else {
		dev_err(&pdev->dev, "%s: failed with rc=%d\n", __func__, rc);
	}
	return rc;
}

/**
 * of_irq_parse_and_map_pci() - Decode a PCI IRQ from the device tree and map to a VIRQ
 * @dev: The PCI device needing an IRQ
 * @slot: PCI slot number; passed when used as map_irq callback. Unused
 * @pin: PCI IRQ pin number; passed when used as map_irq callback. Unused
 *
 * @slot and @pin are unused, but included in the function so that this
 * function can be used directly as the map_irq callback to
 * pci_assign_irq() and struct pci_host_bridge.map_irq pointer
 */
int of_irq_parse_and_map_pci(const struct pci_dev *dev, u8 slot, u8 pin)
{
	struct of_phandle_args oirq;
	int ret;

	ret = of_irq_parse_pci(dev, &oirq);
	if (ret)
		return 0; /* Proper return code 0 == NO_IRQ */

	return irq_create_of_mapping(&oirq);
}
EXPORT_SYMBOL_GPL(of_irq_parse_and_map_pci);
#endif	/* CONFIG_OF_IRQ */

static int pci_parse_request_of_pci_ranges(struct device *dev,
					   struct pci_host_bridge *bridge)
{
	int err, res_valid = 0;
	resource_size_t iobase;
	struct resource_entry *win, *tmp;

	INIT_LIST_HEAD(&bridge->windows);
	INIT_LIST_HEAD(&bridge->dma_ranges);

	err = devm_of_pci_get_host_bridge_resources(dev, &bridge->windows,
						    &bridge->dma_ranges, &iobase);
	if (err)
		return err;

	err = devm_request_pci_bus_resources(dev, &bridge->windows);
	if (err)
		return err;

	resource_list_for_each_entry_safe(win, tmp, &bridge->windows) {
		struct resource *res = win->res;

		switch (resource_type(res)) {
		case IORESOURCE_IO:
			err = devm_pci_remap_iospace(dev, res, iobase);
			if (err) {
				dev_warn(dev, "error %d: failed to map resource %pR\n",
					 err, res);
				resource_list_destroy_entry(win);
			}
			break;
		case IORESOURCE_MEM:
			res_valid |= !(res->flags & IORESOURCE_PREFETCH);

			if (!(res->flags & IORESOURCE_PREFETCH))
				if (upper_32_bits(resource_size(res)))
					dev_warn(dev, "Memory resource size exceeds max for 32 bits\n");

			break;
		}
	}

	if (!res_valid)
		dev_warn(dev, "non-prefetchable memory resource required\n");

	return 0;
}

int devm_of_pci_bridge_init(struct device *dev, struct pci_host_bridge *bridge)
{
	if (!dev->of_node)
		return 0;

	bridge->swizzle_irq = pci_common_swizzle;
	bridge->map_irq = of_irq_parse_and_map_pci;

	return pci_parse_request_of_pci_ranges(dev, bridge);
}

#ifdef CONFIG_PCI_DYNAMIC_OF_NODES

void of_pci_remove_node(struct pci_dev *pdev)
{
	struct device_node *np;

	np = pci_device_to_OF_node(pdev);
	if (!np || !of_node_check_flag(np, OF_DYNAMIC))
		return;
	pdev->dev.of_node = NULL;

	of_changeset_revert(np->data);
	of_changeset_destroy(np->data);
	of_node_put(np);
}

void of_pci_make_dev_node(struct pci_dev *pdev)
{
	struct device_node *ppnode, *np = NULL;
	const char *pci_type;
	struct of_changeset *cset;
	const char *name;
	int ret;

	/*
	 * If there is already a device tree node linked to this device,
	 * return immediately.
	 */
	if (pci_device_to_OF_node(pdev))
		return;

	/* Check if there is device tree node for parent device */
	if (!pdev->bus->self)
		ppnode = pdev->bus->dev.of_node;
	else
		ppnode = pdev->bus->self->dev.of_node;
	if (!ppnode)
		return;

	if (pci_is_bridge(pdev))
		pci_type = "pci";
	else
		pci_type = "dev";

	name = kasprintf(GFP_KERNEL, "%s@%x,%x", pci_type,
			 PCI_SLOT(pdev->devfn), PCI_FUNC(pdev->devfn));
	if (!name)
		return;

	cset = kmalloc(sizeof(*cset), GFP_KERNEL);
	if (!cset)
		goto out_free_name;
	of_changeset_init(cset);

	np = of_changeset_create_node(cset, ppnode, name);
	if (!np)
		goto out_destroy_cset;

	ret = of_pci_add_properties(pdev, cset, np);
	if (ret)
		goto out_free_node;

	ret = of_changeset_apply(cset);
	if (ret)
		goto out_free_node;

	np->data = cset;
	pdev->dev.of_node = np;
	kfree(name);

	return;

out_free_node:
	of_node_put(np);
out_destroy_cset:
	of_changeset_destroy(cset);
	kfree(cset);
out_free_name:
	kfree(name);
}
#endif

/**
 * of_pci_supply_present() - Check if the power supply is present for the PCI
 *				device
 * @np: Device tree node
 *
 * Check if the power supply for the PCI device is present in the device tree
 * node or not.
 *
 * Return: true if at least one power supply exists; false otherwise.
 */
bool of_pci_supply_present(struct device_node *np)
{
	struct property *prop;
	char *supply;

	if (!np)
		return false;

	for_each_property_of_node(np, prop) {
		supply = strrchr(prop->name, '-');
		if (supply && !strcmp(supply, "-supply"))
			return true;
	}

	return false;
}

#endif /* CONFIG_PCI */

/**
 * of_pci_get_max_link_speed - Find the maximum link speed of the given device node.
 * @node: Device tree node with the maximum link speed information.
 *
 * This function will try to find the limitation of link speed by finding
 * a property called "max-link-speed" of the given device node.
 *
 * Return:
 * * > 0	- On success, a maximum link speed.
 * * -EINVAL	- Invalid "max-link-speed" property value, or failure to access
 *		  the property of the device tree node.
 *
 * Returns the associated max link speed from DT, or a negative value if the
 * required property is not found or is invalid.
 */
int of_pci_get_max_link_speed(struct device_node *node)
{
	u32 max_link_speed;

	if (of_property_read_u32(node, "max-link-speed", &max_link_speed) ||
	    max_link_speed == 0 || max_link_speed > 4)
		return -EINVAL;

	return max_link_speed;
}
EXPORT_SYMBOL_GPL(of_pci_get_max_link_speed);

/**
 * of_pci_get_slot_power_limit - Parses the "slot-power-limit-milliwatt"
 *				 property.
 *
 * @node: device tree node with the slot power limit information
 * @slot_power_limit_value: pointer where the value should be stored in PCIe
 *			    Slot Capabilities Register format
 * @slot_power_limit_scale: pointer where the scale should be stored in PCIe
 *			    Slot Capabilities Register format
 *
 * Returns the slot power limit in milliwatts and if @slot_power_limit_value
 * and @slot_power_limit_scale pointers are non-NULL, fills in the value and
 * scale in format used by PCIe Slot Capabilities Register.
 *
 * If the property is not found or is invalid, returns 0.
 */
u32 of_pci_get_slot_power_limit(struct device_node *node,
				u8 *slot_power_limit_value,
				u8 *slot_power_limit_scale)
{
	u32 slot_power_limit_mw;
	u8 value, scale;

	if (of_property_read_u32(node, "slot-power-limit-milliwatt",
				 &slot_power_limit_mw))
		slot_power_limit_mw = 0;

	/* Calculate Slot Power Limit Value and Slot Power Limit Scale */
	if (slot_power_limit_mw == 0) {
		value = 0x00;
		scale = 0;
	} else if (slot_power_limit_mw <= 255) {
		value = slot_power_limit_mw;
		scale = 3;
	} else if (slot_power_limit_mw <= 255*10) {
		value = slot_power_limit_mw / 10;
		scale = 2;
		slot_power_limit_mw = slot_power_limit_mw / 10 * 10;
	} else if (slot_power_limit_mw <= 255*100) {
		value = slot_power_limit_mw / 100;
		scale = 1;
		slot_power_limit_mw = slot_power_limit_mw / 100 * 100;
	} else if (slot_power_limit_mw <= 239*1000) {
		value = slot_power_limit_mw / 1000;
		scale = 0;
		slot_power_limit_mw = slot_power_limit_mw / 1000 * 1000;
	} else if (slot_power_limit_mw < 250*1000) {
		value = 0xEF;
		scale = 0;
		slot_power_limit_mw = 239*1000;
	} else if (slot_power_limit_mw <= 600*1000) {
		value = 0xF0 + (slot_power_limit_mw / 1000 - 250) / 25;
		scale = 0;
		slot_power_limit_mw = slot_power_limit_mw / (1000*25) * (1000*25);
	} else {
		value = 0xFE;
		scale = 0;
		slot_power_limit_mw = 600*1000;
	}

	if (slot_power_limit_value)
		*slot_power_limit_value = value;

	if (slot_power_limit_scale)
		*slot_power_limit_scale = scale;

	return slot_power_limit_mw;
}
EXPORT_SYMBOL_GPL(of_pci_get_slot_power_limit);